Compositions and methods for cross-linking hydratable polymers using produced water

ABSTRACT

Fracturing fluid compositions including a base fluid including a high TDS produced and/or flow back water, brackish water, RO reject water, clear brine, and mixtures thereof with or without added fresh water and systems, and methods for making and using same, where the method includes: (a) adding a first buffer to adjust the pH of a base fluid to an acidic pH, (b) adding a hydratable polymer or polymer slurry to the base fluid to form a hydratable polymer fracturing fluid, (c) adding a cross-linking composition to the hydratable polymer fracturing fluid to form a pre-cross-linked fracturing fluid, and (d) if needed, adding a second buffer to the pre-cross-linked fracturing fluid to adjust the pH of the pre-cross-linked fracturing fluid to form a viscosified fracturing fluid having a crosslinked structure.

RELATED APPLICATIONS

The present application claims priority to and the benefit of U.S.Provisional Application Ser. No. 62/545,368, filed 14 Aug. 2017,incorporated by reference through the operation of the closing paragraphof the specification.

BACKGROUND OF THE DISCLOSURE 1. Field of the Disclosure

Embodiments of the present disclosure relate to compositions, systems,and methods for making and using the compositions, where thecompositions include a crosslinked fracturing fluid including a basefluid comprising a high total dissolved solids (TDS) produced water, aTDS flow back water, a brackish water, a reverse osmosis (RO) rejectwater, a clear brine, and mixtures thereof. Embodiments of the presentdisclosure also relate to low concentration crosslinked polymerfracturing fluid and methods for making and using same with or withoutthe use of high TDS produced water.

In particular, embodiments of the present disclosure relate tocompositions, systems, and methods for making and using thecompositions, where the compositions include a crosslinked fracturingfluids including a base fluid comprising a high TDS produced water, aTDS flow back water, a brackish water, a RO reject water, a clear brine,and mixtures or combinations thereof and in certain embodiments, thebase fluid also includes fresh water. The methods include: (a) adding afirst buffer to the base fluid to lower a pH of the base fluid to form alow pH base fluid, (b) adding a hydratable polymer or a hydratablepolymer slurry to the base fluid to form a hydrated hydratable polymerfracturing fluid, (c) adding a crosslinking agent to the hydratedhydratable polymer fracturing fluid to form a pre-cross-linkedfracturing fluid, and optionally (d) adding a second buffer to thepre-cross-linked fracturing fluid to increase a pH of thepre-cross-linked fracturing fluid to form a viscosified fracturingfluid. In certain embodiments, the methods also include the step ofadding a proppant to the fracturing fluid. In other embodiments, themethods include fracturing a formation with the fracturing fluid of thisdisclosure, where the fracturing methods may include injecting thefracturing fluid with the proppant or injecting a proppant freefracturing fluid followed by injecting a proppant fluid.

2. Description of the Related Art

Hydraulic fracturing is a process in which proppant is transported at avery high pressure along with other necessary reagents to form fractureor fissures in a formation and to prop-open the fractures or fissures inthe formation. The most common way of transporting proppant is bysuspending the proppant in a viscosified fluid. The fluid could beeither viscous (linear gel or crosslinked) or thin as in a “slick waterfrac”. The key is to pump at a higher rate than may leak-off (flow outinto the reservoir rock). When this happens there is a build-up ofpressure at the face exposed to the fracturing fluid. This pressure willcontinue to increase until it exceeds the forces binding the rocktogether. At this point the formation rock will “fracture”. Once thefracture is initiated, continued pumping will cause the fracture to growin length, width and height.

After fracture initiation and during the period of fracture developmentand growth, solids called proppants are added to the fluid being pumpedforming a slurry so that the proppants may be deposited in the createdfracture. Multiple stages of slurry injection at increasing pumpingrates are common. It is the distribution of the solids in the fracturethat will keep the fracture propped open after pumping has ceased andthe formation tries to go back to its unstressed position. This“propped” fracture has a conductivity that is significantly higher thatthe formation rock surrounding it and therefore represents a highlyconductive passageway back to the wellbore.

While the variation in the formation properties of the various producingintervals may lead to the need for a variety of viscosity levels in thefracturing fluids that may be utilized to perform the most effectivefracturing treatment designs, they all have one thing in common. Thatbeing the effect that horizontal completions has had on treatmentdesigns. The trend to horizontal completions has led to the increase ofthe “lateral” lengths and the number of fracturing stages that arerequired to maximize the amount of production that may be realized in agiven well. As the number and size of the stages increases (regardlessof the fluid being utilized) so does the requirement for water that isnecessary to complete the fracture design. This trend may easilytranslate to a fracturing design for a well that could require 5 to 15million gallons of water.

While slick water (containing friction reducers), linear gels andcrosslinked gels all may be effective with fresh water and some limitedblending of fresh and brackish water (containing an elevated level oftotal dissolved solids or TDS), no approach may retain their fluidviscosity (and related proppant transport capability) if TDS levels gettoo high or there is an attempt to utilize produced water, flow backwater, or frac flow back water. This is because of high TDS of producedor flow back water which translates to a large number of water analytesor impurities compared to fresh water. While linear gels may maintaintheir viscosity and transport properties in high TDS fluids the same maynot be said for the friction reducers that are a key part of a slickwater design or a crosslinked polymer gel.

The effect that high TDS water has on the performance properties of thefriction reducer (used in slick water designs) may be illustrated by theresults of a dynamic proppant transport test. The procedure for such atest is shown below:

-   -   1. adding a 500 mL sample of a hydrated friction reducer/frac        system to be tested to a blend jar including a blender and stir        for 5 minutes to 1500 rpm (i.e., the time allowed for polymer        hydration may be representative of an expected hydration period        (associated with the treatment) or some standard period);    -   2. adding 120 g of a proppant to be tested (equivalent to 2 ppg)        and mix for 30 seconds;    -   3. increasing a shear rate to achieve a calculated high shear        history (i.e., the shear history may be specific to a particular        application or some standard calculated shear history);    -   4. at the conclusion of the high shear history, reducing the        blender rpm until build-up of proppant is visible on the bottom        of the blend jar;    -   5. increasing the rpm to fluidize the settled proppant and then        start decreasing rpm to again find a minimum rpm (i.e., for a        friction reducer to exhibit an improved proppant transport the        RPM reading needs to be a minimum of 10% lower than that of the        same TDS water without a friction reducer) to prevent proppant        build-up and repeating this process until the minimum rpm        numbers remains within 10% of one another; and    -   6. recording a lowest rpm reading that does not cause proppant        build up.

The adverse effect that high TDS waters have on the suspensionproperties of a friction reducer are illustrated in FIG. 1. The testresults shown in FIG. 1 verify that an increase of TDS to 50,000 ppmwill result in the total elimination of any (anionic or cationic)friction reducer's ability to improve proppant transport above the sameTDS water without any polymer in solution.

Slick water fracturing designs are the most frequently utilized approachto fracture stimulating today's horizontal completion that continue toutilize massive amounts of fresh water. Their popularity is based ontheir relatively low cost coupled with their ability to create long,narrow fracture profiles. The desire to improve the well's response tothis stimulation technique has resulted in an increase in the length ofthe lateral completion and in the number of stages performed in eachtreatment design. Both of these trends result in an increase in theamount of fresh water that is consumed in each stimulation operation.

There is increasing pressure to reduce the amount of fresh water that isconsumed in the fracturing process. An obvious alternative would be toutilize high TDS water or at least a mixture of high TDS and fresh wateras a replacement for fresh water in these fracturing operations.Unfortunately, the effect of elevated TDS on the viscosity and transportcapability of a slick water fluid makes this approach less thandesirable. The effect of high TDS on friction reducers is best shown inFIG. 1. The samples labeled AFRE-4 represent tests performed on a highmolecular weight/high viscosity anionic friction reducer available fromPfP Industries.

All test results depicted in FIG. 1 include a high shear period thatrepresents the high velocity period corresponding to the fracturingfluid traveling through tubular good from the surface to the entry ofthe fracture. This representative shear history will test each frictionreducer's capacity to resist shear degradation. The combination of highTDS and a representative shear history renders both the high viscosityanionic friction reducers and standard cationic friction reducerscomparable (in suspension properties) to a high TDS water that does notcontain a friction reducer/polymer to improve proppant transport.

A crosslinked fracturing fluid may be described as consisting of ahydratable polymer such as guar, its derivatives, or a naturalpolysaccharide that hydrates easily in water and may be cross-linkedwith metals or polyvalent compounds to form an efficient, effective,carrier of proppant into fractured formations. Traditionally, this typeof fracturing fluid would include hydratable polymers such as guar, a pHbuffer, and cross-linking compositions (such as a borate cross-linker).The traditional method for forming the fracturing fluid includes: (a)hydrating a hydratable polymer or hydratable polymer slurry in a pHneutral water, (b) adding a high pH buffer to the fluid to increase a pHof the fluid to a pH above pH 9, and (c) adding a cross-linkingcomposition to the fluid to cross-link the hydratable polymers to formthe viscosified fracturing fluid.

This type of fracturing fluid approach (unlike a slick water design)will possess a significant ability to generate fracture width andtransport proppant if prepared using a relatively fresh water (low TDS)but if prepared using a high TDS water will result in a poor viscosityand minimum proppant transport capability as demonstrated by the datapresented in FIG. 2.

FIG. 2 confirms the viscosity profile of a crosslinked polymer preparedwith fresh water. Switching from fresh water to a higher TDS syntheticbrine (in this case API brine which has approximately 110,000 ppm TDS)drops the viscosity by more than 50%. Even more interesting is that ifyou actually utilize a produced back water (instead of a synthetic brinewith a similar TDS) the viscosity drops to approximately 5% of the valuefor the same system in fresh water.

The continued growth in horizontal completions and in the desire toincrease the amount of proppant pumped into the fracture matrix willresult an increased need of water to be used in the fracturing programs.This trend is already causing a concern in the amount of fresh waterthat is required to meet fracturing needs and that will only continue togrow. At some point it will become a necessity to fill some of therequired volume with something other than fresh water. Produced waterfrom the formation or produced back water (after a fracturing treatment)are something that currently requires a monitored disposal plan andprocess. Utilizing these water sources as part or all of the water (tobe consumed in a fracturing treatment) will both decrease the freshwater requirement and offer an alternative to current disposal costs.

However, increasing the TDS of the water (to be utilized in a fracturingprogram) will create its own set of issues. In slick water design whileincreased TDS has minimal effect on the drag reduction (that may beachieved during a pumping operation), as shown in FIG. 1 it will alsorender both anionic and cationic friction reducers virtually incapableof significantly contributing to proppant transport. As shown in FIG. 2,high TDS will also impact the viscosity values that may be achieved andproppant transport capabilities that may be derived from crosslinkedpolymer systems.

Clearly there is a need to incorporate high TDS water in fracturingtreatment designs that may replace either current crosslinked fluidsystems (designed to transport and place high concentrations ofproppant) or slick water systems that may still create the longrelatively narrow propped fractures that are required to maximize wellresponse in today's well. In the case of slick water systems, there isalso a clear need to create a viable option to the high volume, highrate slick water treatment designs that result in a less than desirablepropped fracture length.

SUMMARY OF THE DISCLOSURE

Embodiments of this disclosure provide fracturing fluid compositionsincluding: (a) a base fluid, (b) a first buffer to adjust a pH of thebase fluid to a target pH value, (c) a dry powdered hydratable polymeror a hydratable polymer slurry, (d) a cross-linking composition, and (e)an optional second buffer to increase the pH to a pH above pH 9 forcross-linking compositions that require a high final pH. The firstbuffer is adapted to lower the pH of the base fluid prior to adding thepolymer or polymer slurry and the cross-linking composition to the basefluid, while the second buffer is adapted to raise the pH after theaddition of the polymer or polymer slurry and the cross-linkingcomposition to form a crosslinked or viscosified fracturing fluid.

In certain embodiments, the fracturing fluid compositions may notrequire addition of the second buffer as the fracturing fluidviscosifies at a final pH that is below a pH of 7. In such compositions,there may not be a requirement to achieve a final pH adjustment (afterthe addition of the polymer or polymer slurry and the cross-linkingcomposition). In other embodiments, the crosslinked compositions arebased on reduced polymer concentration levels (generally<10 ppt) toachieve a controlled viscosity level that will be an efficient andeffective alternative to a slickwater treatment design.

Embodiments of this disclosure provide systems for using fracturingfluids of this disclosure, where the systems include: (1) a vesselcontaining a fracturing fluid including: (a) a base fluid, (b) a firstbuffer to adjust a pH of the base fluid to a target pH value, (c) a drypowdered hydratable polymer or a hydratable polymer slurry, (d) across-linking composition, and (e) an optional second buffer to increasethe pH to a pH above pH 9, wherein the pH is lowered to prior to addingthe slurry and the cross-linking composition, and the pH is raised afterthe addition of the slurry and the cross-linking composition to form aviscosified fracturing fluid; and (2) an injection assembly forinjecting the fracturing fluid from the vessel into a formation underfracturing conditions to fracture the formation. In other embodiments ofthis disclosure, the systems include: (1) a vessel containing afracturing fluid including: (a) a base fluid, (b) a first buffer toadjust a pH of the base fluid to a target pH value, (c) a hydratablepolymer slurry, (d) a cross-linking composition or mixtures that do notrequire the pH to be elevated by an additional or a second pH buffer and(2) an injection assembly for injecting the fracturing fluid from thevessel into a formation under fracturing conditions to fracture theformation. Embodiments are disclosed for formulating both high and lowfinal pH crosslinkable polymer fracturing fluids, wherein the fluidshave a greatly reduced polymer loading allowing a reduced targeted lowerviscosity to be achieved.

In other embodiments, the systems are based on using a crosslinkedfracturing fluid having a final pH that is less than or equal to pH 7.In such systems, the fracturing fluid may not require a final pHadjustment (after the addition of the slurry and crosslinker). In yetother embodiments, the systems are based on using a crosslinkedfracturing fluid composition having a reduced polymer concentrationlevel, generally, <10 ppt to achieve a controlled viscosity level thatwill be an efficient and effective alternative to a slickwater treatmentdesign. In other embodiments, the fracturing fluid includes a proppant.In other embodiments, the systems include a fracture fluid vessel and aproppant containing fluid vessel and the injection assembly sequentiallyinjects the proppant free fracturing fluid followed by the proppantcontaining fluid under fracturing conditions.

Embodiments of this disclosure provide methods for forming fracturingfluids based on an aqueous base fluid, where the methods include: (a)adding a first buffer to the aqueous base fluid to lower a pH of thebase fluid to form a low pH base fluid, (b) adding a hydratable polymeror hydratable polymer slurry to the low pH base fluid to form ahydratable polymer fracturing fluid, (c) adding a cross-linkingcomposition to the hydratable polymer fracturing fluid to form apre-cross-linked fracturing fluid, and (d) optionally adding a secondbuffer to the pre-cross-linked fracturing fluid to increase a pH of thepre-cross-linked fracturing fluid to form a viscosified fracturingfluid. In certain embodiments, the methods also include the step ofadding a proppant to the fracturing fluid. In other embodiments, themethods include fracturing a formation with a fracturing fluid of thisdisclosure, where the methods further includes injecting the fracturingfluid with the proppant or injecting a proppant free fracturing fluidfollowed by injecting a proppant fluid.

Embodiments of this disclosure provide methods for fracturing aformation using an aqueous high TDS base fluid, where the methodsinclude forming a fracturing fluid including: (a) adding a first bufferto the aqueous high TDS base fluid to lower a pH of the aqueous high TDSbase fluid to form a low pH aqueous high TDS base fluid, (b) adding ahydratable polymer or hydratable polymer slurry to the low pH aqueoushigh TDS base fluid to form a hydratable polymer fracturing fluid, (c)adding a cross-linking composition to the hydratable polymer fracturingfluid to form a pre-cross-linked fracturing fluid, and (d) optionallyadding a second buffer to the pre-cross-linked fracturing fluid toincrease a pH of the pre-cross-linked fracturing fluid to form aviscosified fracturing fluid. The methods also include injecting thefluid into a formation under fracturing conditions sufficient tofracture the formation. In certain embodiments, the methods also includethe step of adding a proppant to the fracturing fluid prior to theinjecting step. In other embodiments, the methods include injecting aproppant free fracturing fluid into the formation followed by injectinga proppant containing fluid into the formation under fracturingconditions.

BRIEF DESCRIPTION OF THE DRAWINGS OF THE DISCLOSURE

The disclosure may be better understood with reference to the followingdetailed description together with the appended illustrative drawings inwhich like elements are numbered the same:

FIG. 1 depicts a plot of minimum rpm tests of fracturing fluids based ondifferent base fluids in high shear periods.

FIG. 2 depicts the viscosity profiles of a crosslinked fluids based ondifferent base fluids.

FIG. 3 depicts the behavior of a fracturing fluid of this disclosure.

FIG. 4 depicts viscosities of a fracturing fluid of this disclosureusing different waters, where PW1 is a first produced water, FB1 is aflowback water, PW2 is a second produced water, PW3 is a third producedwater, PW4 is a fourth produced water, SWD1 is a disposal salt water,PW5 is a fifth produced water, and PW6 is a sixth produced water andwhere the loading is in gpt (gallons per thousand gallons).

FIG. 5 depicts a plot of minimum rpm tests of fracturing fluids of thisdisclosure in high shear periods.

FIG. 6 depicts a plot of minimum rpm tests of fracturing fluids of thisdisclosure in high shear periods.

FIG. 7 depicts a plot of minimum rpm tests of fracturing fluids of thisdisclosure in high shear periods.

FIG. 8 depicts a testing system for testing the flow characteristics ofthe fluids.

FIG. 9 depicts a comparison between the fracturing fluids of thisdisclosure and conventional fracturing fluids.

DEFINITIONS USED IN THE DISCLOSURE

In addition to having their customary and usual meaning, the followingdefinitions apply where the context permits in the specification andclaims:

The term “at least one” means one or more or one or a plurality,additionally, these three terms may be used interchangeably within thisapplication. For example, at least one device means one or more devicesor one device and a plurality of devices.

The term “one or a plurality” means one item or a plurality of items.

The term “about” means that a value of a given quantity is within ±20%of the stated value. In other embodiments, the value is within ±15% ofthe stated value. In other embodiments, the value is within ±10% of thestated value. In other embodiments, the value is within ±7.5% of thestated value. In other embodiments, the value is within ±5% of thestated value. In other embodiments, the value is within ±2.5% of thestated value. In other embodiments, the value is within ±1% of thestated value.

The term “substantially” means that a value of a given quantity iswithin±5% of the stated value. In other embodiments, the value is within±2.5% of the stated value. In other embodiments, the value is within ±2%of the stated value. In other embodiments, the value is within ±1% ofthe stated value. In other embodiments, the value is within ±0.5% of thestated value. In other embodiments, the value is within ±0.1% of thestated value.

The term “gpt” means gallons per thousand gallons.

The term “gptg” means gallons per thousand gallons.

The term “pptg” or “ppt” means pounds per thousand gallons.

The term “wt. %” means weight percent.

The term “w/w” means weight per weight.

The term “ppm” means parts per million.

The term “cps” or “cP” means centipoise.

The term “rpm” means revolutions per minute.

The term “TDS” means total dissolved solids and means waters having fromabout 60 ppm to about 120,000 ppm total dissolved solids.

The term “RO” means reverse osmosis.

The term “FR” means friction reducer.

The term “fracturing” refers to the process and methods of breaking downa geological formation, i.e., the rock formation around a well bore, bypumping fluid at very high pressures, in order to increase productionrates from a hydrocarbon reservoir. The fracturing methods of thisdisclosure use otherwise conventional techniques known in the art.

The term “under fracturing conditions” means injecting or pumping afracturing fluid into a formation at a sufficient pressure, at asufficient temperature (normally not an issue), and for a timesufficient to form fractures or fissures in the formation.

The term “proppant” refers to a granular substance suspended in thefracturing fluid during the fracturing operation, which serves to keepthe formation from closing back down upon itself once the pressure isreleased. Proppants envisioned by the present disclosure include, butare not limited to, conventional proppants familiar to those skilled inthe art such as sand, 20-40 mesh sand, resin-coated sand, sinteredbauxite, glass beads, and similar materials.

DETAILED DESCRIPTION OF THE DISCLOSURE

The inventors have found that compositions, systems, and methods forforming and using fracturing fluids, where the fracturing fluids arebased on aqueous base fluids including high TDS produced water and/orflow back water and/or disposal water and/or mixtures of fresh water.The compositions, systems, and methods may be formulated andimplemented, where the compositions, systems, and methods are based onadjusting a pH of the aqueous base fluids to a sufficiently low pH toform a low pH base fluid, adding a hydratable polymer or hydratablepolymer slurry to the base fluid to form a fracturing fluid, adding across-linking composition to the fracturing fluid to form apre-cross-linked fracturing fluid, and then optionally (if utilizing ahigh pH crosslinking system) adjusting the pH of the pre-cross-linkedfracturing fluid to a pH above pH 9 to from a crosslinked fracturingfluid. In certain embodiments, the methods also include adding aproppant to the crosslinked fracturing fluid. In other embodiment, themethods may also include adding a breaking composition to the fracturingfluids to break the viscosity of the fracturing fluids.

The compositions, systems, and methods of this disclosure are designedto overcome the problems associated with using high TDS (total dissolvedsolids) waters including produced and/or flow back water and/or disposalwater in fracturing fluids, which will allow the use and reuse oftreated and untreated produced water with or without the addition offresh water. The inventors have found that, contrary to existingknowledge and practices, cross-linked hydratable polymer basedfracturing fluids may be produced using produced, flow back, and/orfracturing flow back water or mixtures of these waters and fresh water.In certain embodiments, the hydratable polymers are guar and/or guarderivatives and the cross-linking composition comprises a boratecross-linkers or combinations of borate crosslinkers or crosslinkersthat are compatible with low pH approaches to crosslinking To that end,we re-engineered the cross-linking process and designed buffers tohandle the severity of high TDS fluids such as produced and/or flow backwater and/or disposal water. One such process includes the followingsteps: (a) adding a first buffer to an aqueous base fluid including ahigh TDS water to lower a pH of the aqueous base fluid to form a low pHbase fluid; (b) adding a hydratable polymer or hydratable polymer slurryto the base fluid to form a fracturing fluid; (c) adding a cross-linkingcomposition to the fracturing fluid to form a pre-cross-linkedfracturing fluid; and optionally (if the crosslinked system beingutilized requires high pH) (d) adding a second buffer to increase the pHof the pre-cross-linked fracturing fluid to form a crosslinkedfracturing fluid.

In certain embodiments, the first buffer is added to the base fluid at alevel sufficient to adjust a pH of the base fluid to an acidic pH. Incertain embodiments, the acidic pH is less than or equal to pH 7. Inother embodiments, the acidic pH is less than or equal to pH 6. In otherembodiments, the acidic pH is less than or equal to pH 5. In otherembodiments, the acidic pH is less than or equal to pH 4. The buffer mayinclude an inorganic acid, an organic acid, or mixtures thereof. Thefirst buffer is added until the pH is at an acidic level for example ator below pH 7, 6, 5, or 4. In certain embodiments, an amount of theadded first buffer is between about 0.1 gpt and about 5 gpt depending onthe initial pH of the base fluid.

In certain embodiments where a high pH is needed, a second buffer isadded to the fracturing fluid after the polymer or the polymer slurryand the crosslinking composition have been added at a level sufficientto adjust a pH of the fracturing fluid to at or below pH 9. The secondbuffer may include an inorganic base, an organic base, or mixturesthereof. The second buffer is added until the pH is at or below pH 9. Incertain embodiments, an amount of the added second buffer is betweenabout 0.1 gpt and about 5 gpt depending on the initial pH of thefracturing fluid. As the pH of the fracturing fluid prior to addition ofthe second buffer is considerably below pH 9, cross-linking of thefracturing fluid does not start to occur until the pH of the fluidapproaches pH 9 or greater. Thus, the compositions have a build incross-link delay system, which is one of the unique features of thecompositions, systems, and/or methods of this disclosure.

The compositions, systems and methods also provide systems thatincorporate a crosslinked polymer approach based on a final pH that isbelow pH 7. In such systems, it may not be necessary to make a final pHadjustment (after the addition of the polymer or the polymer slurry andthe crosslinking composition). Still other compositions, systems andmethods will provide approaches in which the crosslinked compositionsare based on reduced polymer concentration levels of <10 ppt to achievea controlled viscosity that will result in the generation of the desiredlong narrow type fractures, but with superior proppant transport ascompared to low viscosity slick water designs and therefore increasedpropped fracture length.

Embodiments of the present disclosure broadly relates to fracturingfluid compositions including: (a) a base fluid comprising an elevatedtotal dissolved solids (TDS) water selected from the group consisting toproduced, flow back water, brackish water, reverse osmosis (RO) rejectwater, clear brine, and mixtures and combinations thereof, (b) a firstbuffer, (c) a hydratable polymer or a hydratable polymer slurry, and (d)a cross-linking composition, wherein the first buffer is adapted toadjust a pH of the base fluid to an acidic pH prior to adding thehydratable polymer or the hydratable polymer slurry and thecross-linking composition to the base fluid to reduce or preventpre-mature polymer crosslinking, and wherein the cross-linkingcomposition crosslinks the hydratable polymer after hydration to formthe fracturing fluid composition having a crosslinked structure. Incertain embodiments, the compositions may also include (e) a secondbuffer to adjust the pH to a final pH sufficient to activate thecrosslinking composition toe form the crosslinked structure in thecomposition. In other embodiments, the second buffer adjusts the pH toat or above 9. In other embodiments, the base fluid further includesfresh water. In other embodiments, the the hydratable polymer isselected from the group consisting of galactomannan gums, glucomannangums, guars, derivatized guars, cellulose derivatives, syntheticpolymers such as polyvinyl alcohol, polyacrylamides,poly-2-amino-2-methyl propane sulfonic acid, other synthetic polymersand copolymers, and mixtures or combinations thereof. In otherembodiments, the the hydratable polymer is a guar or derivatized guarand is in powder form when added to the composition or to the slurry. Inother embodiments, the hydratable polymer is a mixture of a guar orderivatized guar and a polyacrylamide in which the polyacrylamide ispresent in an amount between 5 wt. % and 20 wt. % of the total polymerweight, and the polyacrylamide reduces a drag of the composition beingpumped through a tubular downhole injection mechanism into a formationto be fracture and improves a shear stability of the crosslinkedstructure formed in the composition. In other embodiments, the thehydratable polymer is present in an amount between about 0.05 wt. % andabout 0.5 wt. % in the composition or if in a slurry form, the polymeris present in an amount between about 1 gpt and about 10 gpt in theslurry. In other embodiments, the the amount is between about 0.05 wt. %and about 0.10 wt. % in the composition or between about 1 gpt and 2 gptin the slurry. In other embodiments, the the acidic pH is less than orequal to pH 7, or less than or equal to pH 6, or less than or equal topH 5, or less than or equal to pH 4. In other embodiments, thecrosslinking composition is capable of producing the crosslinkedstructure at the acidic pH. In other embodiments, the crosslinkingcomposition comprises compounds including boron ions, zirconium ions,and titanium ions, or mixtures thereof. In other embodiments, thecrosslinking composition comprises one or more borate compounds.

Embodiments of the present disclosure broadly relates to methods offracturing a subterranean formation including pumping a fracturing fluidcompositions including (a) a base fluid comprising an elevated totaldissolved solids (TDS) water selected from the group consisting toproduced, flow back water, brackish water, reverse osmosis (RO) rejectwater, clear brine, and mixtures and combinations thereof, (b) a firstbuffer, (c) a hydratable polymer or a hydratable polymer slurry, and (d)a cross-linking composition, wherein the first buffer is adapted toadjust a pH of the base fluid to an acidic pH prior to adding thehydratable polymer or the hydratable polymer slurry and thecross-linking composition so that the polymer may hydrate but notcrosslink, and wherein the cross-linking composition crosslinks thehydratable polymer to form the fracturing fluid composition having acrosslinked structure. In certain embodiments, the composition used inthe methods may also include a second buffer to adjust the pH to a finalpH sufficient to activate the crosslinking composition. In otherembodiments, the second buffer adjusts the pH to at or above 9. In otherembodiments, the base fluid further includes fresh water. In otherembodiments, the methods may further include adding a proppant to thefracturing fluid being pumped into the well. In other embodiments, thehydratable polymer can be taken from a group that includes galactomannangums, glucomannan gums, guars, derivatized guars, cellulose derivatives,synthetic polymers such as polyvinyl alcohol, polyacrylamides,poly-2-amino-2-methyl propane sulfonic acid, and various other syntheticpolymers and copolymers and mixtures or combinations thereof. In otherembodiments, the hydratable polymer is a guar or derivatized guar and isin powder form when added to the composition or to the slurry. In otherembodiments, the hydratable polymer is a mixture of a guar orderivatized guar and a polyacrylamide in which the polyacrylamide ispresent in an amount between 5 wt. % and 20 wt. % of the total polymerweight, and the polyacrylamide reduces a drag of the composition beingpumped through a tubular downhole injection mechanism into a formationto be fracture and improves a shear stability of the crosslinkedstructure formed in the composition In other embodiments, the hydratablepolymer is present in an amount between about 0.05 wt. % and about 0.5wt. % in the composition or if in a slurry form, the polymer is presentin an amount between about 1 gpt and about 10 gpt in the slurry. Inother embodiments, the amount is between about 0.05 wt. % and about 0.10wt. % in the composition or between about 1 gpt and 2 gpt in the slurry.In other embodiments, the acidic pH is less than or equal to pH 7, orless than or equal to pH 6, or less than or equal to pH 5, or less thanor equal to pH 4. In other embodiments, the crosslinking composition iscapable of producing the crosslinked structure at the acidic pH. Inother embodiments, the crosslinking composition is comprised of metalions including boron, zirconium, and titanium containing compounds, ormixtures thereof. In other embodiments, the crosslinking compositioncomprises one or more borate compounds.

SUITABLE REAGENTS USED IN THE DISCLOSURE Aqueous Base Fluids

Suitable aqueous base fluids include, without limitation, a high TDSproduced water, a high TDS flow back water, a high TDS fracturing flowback water, a brackish water, a reverse osmosis (RO) reject water, aclear brine, and mixtures thereof. In certain embodiments, the aqueousbase fluids further include fresh water.

Hydratable Polymers

Suitable hydratable polymers or gelling agents that may be used in thedisclosure include, without limitation, any hydratable polysaccharidesthat are capable of forming a gel in the presence of a crosslinkingagent. Exemplary examples of hydratable polysaccharides include, withoutlimitation, galactomannan gums, glucomannan gums, guars, derivatizedguars, cellulose derivatives, and mixtures or combinations thereof.Specific examples are guar gum, guar gum derivatives, locust bean gum,Karaya gum, carboxymethyl cellulose, carboxymethyl hydroxyethylcellulose, and hydroxyethyl cellulose. Other specific examples include,without limitation, guar gums, hydroxypropyl guar, carboxymethylhydroxypropyl guar, carboxymethyl guar, and carboxymethyl hydroxyethylcellulose. Suitable hydratable polymers may also include syntheticpolymers, such as polyvinyl alcohol, polyacrylamides,poly-2-amino-2-methyl propane sulfonic acid, and various other syntheticpolymers and copolymers. In certain embodiments, the molecular weight ofthe hydratable synthetic polymers are between about 10,000 to about100,000,000. In other embodiments, the molecular weight is between about10,000 to about 10,000,000. In other embodiments, the molecular weightis between about 10,000 to about 1,000,000.

The hydratable polymer may be present in a fracturing fluid inconcentrations ranging from about 0.05 wt. % to about 10 wt. %. Incertain embodiments, the polymer concentration ranges between about 0.10wt. % and about 5.0 wt. %. In other embodiments, the polymerconcentration ranges between about 0.05 w.% and about 0.7 wt. % of theaqueous fluid. In certain embodiments, the hydratable polymer is presentin a range from about 0.10 wt. % to about 0.25 wt1.%. If the polymer isin the form or a slurry, then the slurry is present in an amount betweenabout 10 gpt and about 30 gpt (gallons per thousand gallons) of thefracturing fluid. In certain embodiments, the polymer slurry amount isbetween about 1 gpt and about 15 gpt. In other embodiments, the polymerslurry amount is between about between about 2 gpt and about 5 gpt.

Crosslinking Agents

Suitable crosslinking agents include, without limitation, any compoundthat increases the viscosity of a fluid including the hydratablepolymers by chemical crosslinks, physical crosslinks, and/or cross-linksthe hydratable polymer by any other mechanism. For example, the gelationof a hydratable polymer may be achieved by cross-linking the polymerwith metal ions including boron, zirconium, and titanium containingcompounds, or mixtures thereof. One class of suitable crosslinkingagents is organotitanates. Another class of suitable crosslinking agentsis borates. The selection of an appropriate crosslinking agent dependsupon the type of treatment to be performed and the hydratable polymer tobe used. The amount of the crosslinking agent used also depends upon thewell conditions and the type of treatment to be introduced. However, therange is generally from about 10 ppm to about 1000 ppm of metal ion ofthe crosslinking agent in the hydratable polymer fluid.

Other crosslinking agents may be a borate-containing compounds,titanate-containing compounds, zirconium-containing compound, andmixtures thereof. For example, the crosslinking agent can be sodiumborate×H₂O (varying waters of hydration), boric acid, boratecrosslinkers (a mixture of a titanate constituent, preferably anorganotitanate constituent, with a boron constituent. The organotitanateconstituent can be TYZOR® titanium chelate esters from E.I du Pont deNemours & Company. The organotitanate constituent can be a mixture of afirst organotitanate compound having a lactate base and a secondorganotitanate compound having triethanolamine base. The boronconstituent can be selected from the group consisting of boric acid,sodium tetraborate, and mixtures thereof. These are described in U.S.Pat. No. 4,514,309, incorporated herein by reference, borate based oressuch as ulexite and colemanite, Ti(IV) acetylacetonate, Ti(IV)triethanolamine, Zr lactate, Zr triethanolamine, Zrlactate-triethanolamine, Zr lactate-triethanolamine-triisopropanolamine,or mixtures thereof. In some embodiments, the well treatment fluidcomposition may further comprise a proppant.

Yet other crosslinking agents that crosslink polymer to even higherviscosities and more effective at carrying proppant into the fracturedformation. The borate ion has been used extensively as a crosslinkingagent, typically in high pH fluids, for guar, guar derivatives and othergalactomannans. See, for example, U.S. Pat. No. 3,059,909, incorporatedherein by reference and numerous other patents that describe thisclassic aqueous gel as a fracture fluid. Other crosslinking agentsinclude, for example, titanium crosslinkers (U.S. Pat. No. 3,888,312,incorporated herein by reference), chromium, iron, aluminum, andzirconium (U.S. Pat. No. 3,301,723, incorporated herein by reference).Of these, the titanium and zirconium crosslinking agents are typicallypreferred. Examples of commonly used zirconium crosslinking agentsinclude zirconium triethanolamine complexes, zirconium acetylacetonate,zirconium lactate, zirconium carbonate, and chelants of organicalphahydroxycorboxylic acid and zirconium. Examples of commonly usedtitanium crosslinking agents include titanium triethanolamine complexes,titanium acetylacetonate, titanium lactate, and chelants of organicalphahydroxycorboxylic acid and titanium. The crosslinking compositionsmay include mixtures or combination of any of crosslinking agentsdisclosed herein.

Proppants

Suitable propping agents or proppants are typically added to thefracturing fluid prior to the addition of a crosslinking agent. However,proppants may be introduced in any manner which achieves the desiredresult. Any proppant may be used in embodiments of the disclosure.Examples of suitable proppants include, but are not limited to, quartzsand grains, glass and ceramic beads, walnut shell fragments, aluminumpellets, nylon pellets, and the like. Proppants are typically used inconcentrations between about 1 lb to about 8 lbs. per gallon of afracturing fluid, although higher or lower concentrations may also beused as desired. The fracturing fluid may also contain other additives,such as surfactants, corrosion inhibitors, mutual solvents, stabilizers,paraffin inhibitors, tracers to monitor fluid flow back, and so on.

Breaking Agents

The term “breaking agent” or “breaker” refers to any chemical that iscapable of reducing the viscosity of a gelled or crosslinked fluid. Asdescribed above, after a fracturing fluid is formed and pumped into asubterranean formation, it is generally desirable to convert the highlyviscous gel to a lower viscosity fluid. This allows the fluid to beeasily and effectively removed from the formation and to allow desiredmaterial, such as oil or gas, to flow through the proppant packedfracture into the well bore. This reduction in viscosity of the treatingfluid is commonly referred to as “breaking” The reduction in viscositymay be attributable to breaking the crosslinked structure, degrading thebase polymer being used or a combination of both mechanisms.Consequently, the chemicals used to break the viscosity of the fluid isreferred to as a breaking agent or a breaker.

Examples of inorganic breaking agents for use in this invention include,but are not limited to, persulfates, percarbonates, perborates,peroxides, perphosphates, permanganates, etc. Specific examples ofinorganic breaking agents include, but are not limited to, alkalineearth metal persulfates, alkaline earth metal percarbonates, alkalineearth metal perborates, alkaline earth metal peroxides, alkaline earthmetal perphosphates, zinc salts of peroxide, perphosphate, perborate,and percarbonate, and so on. Additional suitable breaking agents aredisclosed in U.S. Pat. Nos. 5,877,127; 5,649,596; 5,669,447; 5,624,886;5,106,518; 6,162,766; and 5,807,812, incorporated herein by reference.In some embodiments, an inorganic breaking agent is selected fromalkaline earth metal or transition metal-based oxidizing agents, such asmagnesium peroxides, zinc peroxides, and calcium peroxides.

In addition, enzymatic breakers may also be used in place of or inaddition to a non-enzymatic breaker. Examples of suitable enzymaticbreakers such as guar specific enzymes, alpha and beta amylases,amyloglucosidase, aligoglucosidase, invertase, maltase, cellulase, andhemi-cellulase are disclosed in U.S. Pat. Nos. 5,806,597 and 5,067,566,incorporated herein by reference.

A breaking agent or breaker may be used “as is” or be encapsulated andactivated by a variety of mechanisms including crushing by formationclosure or dissolution by formation fluids. Such techniques aredisclosed, for example, in U.S. Pat. Nos. 4,506,734; 4,741,401;5,110,486; and 3,163,219, incorporated herein by reference.

Inorganic Acids

Suitable inorganic acids include, without limitation, any inorganicacid. Exemplary examples include, without limitation, hydrogen chloride,sulfuric acid, phosphoric acid, or mixtures thereof.

Organic Acids

Suitable organic acids include, without limitation, any organic acid.Exemplary examples include, without limitation, formic acid, aceticacid, propionic acid, or mixtures thereof

Inorganic Bases

Suitable inorganic bases include, without limitation, any inorganicbase. Exemplary examples include, without limitation, sodium hydroxide,sodium bicarbonate, sodium carbonate, sodium bicarbonate, potassiumhydroxide, potassium bicarbonate, potassium carbonate, or mixturesthereof.

Organic Bases

Suitable organic acids include, without limitation, any organic base.Exemplary examples include, without limitation, sodium tert-butoxide,potassium tert-butoxide, choline hydroxide, or mixtures thereof.

Friction Reducing Agents

Suitable friction reducing agents include, without limitation, highmolecular weight, anionic polymers having a molecular weight of aboveabout 15 million, or ranging from about 18 million to about 40 millionor ranging from about 18 million to about 25 million. Most standardpolymers useful as friction reducers for oil and gas field stimulationexhibit a molecular weight within the range of about 10 to about 12million. Exemplary example of high molecular weight, anionic polymersinclude, without limitation, hydrolyzed or partially hydrolyzedpolyacrylic acid, hydrolyzed or partially hydrolyzed polymethacrylicacid, hydrolyzed or partially hydrolyzed polyacrylamide, hydrolyzed orpartially hydrolyzed copolymers including acrylic acid, methyacrylicacid, and/or acrylamide with other ethylenically unsaturated monomersincluding vinyl alcohol, ethylene, propylene, etc. and mixtures andcombinations thereof. In certain embodiments, the friction reducingagents include partially hydrolyzed polyacylamide (PHPA).

Nonionic and Amphoteric Polymers

Suitable nonionic and amphoteric polymers used in the presentcomposition preferably exhibit a molecular weight within the range ofabout 8 million to about 14 million or ranging from about 10 million to15 million or ranging from about 10 million to about 12 million.Additional information on this mixture of friction-reducing polymers forhigh TDS systems is disclosed in copending U.S. patent application Ser.No. 15/786,769 the disclosure of which is hereby incorporated byreference.

Exemplary polymers (anionic, cationic, or amphoteric) may also behomopolymers, copolymers, terpolymers, or high order mixed monomerpolymers synthesized from one or more anionic monomers, cationicmonomers, and/or neutral monomers. For copolymer and high order mixedmonomer polymers, the monomers used may have similar reactivities sothat the resultant amphoteric polymeric material has a randomdistribution of monomers. The anionic monomers may be any anionicmonomer such as acrylic acid, methacrylic acid,2-acrylamide-2-methylpropane sulfonic acid, and/or maleic anhydride. Thecationic monomer may be any cationic monomer such as dimethyl-diallylammonium chloride, dimethylamino-ethyl methacrylate, and/orallyltrimethyl ammonium chloride. The neutral monomer may be any neutralmonomer such as butadiene, N-vinyl-2-pyrrolidone, methyl vinyl ether,methyl acrylate, maleic anhydride, styrene, vinyl acetate, acrylamide,methyl methacrylate, and/or acrylonitrile. Other exemplary polymers maybe a terpolymer synthesized from acrylic acid (AA), dimethyl diallylammonium chloride (DMDAC) or diallyl dimethyl ammonium chloride(DADMAC), and acrylamide (AM). The ratio of monomers in the terpolymercan generally be any ratio. A presently preferred ratio is about 1:1:1.Other exemplary amphoteric polymeric materials include approximately 30%polymerized AA, 40% polymerized AM, and 10% polymerized DMDAC or DADMACwith approximately 20% free residual DMDAC or DADMAC which is notpolymerized due to lower relative reactivity of the DMDAC or DADMACmonomer.

EXPERIMENTS OF THE DISCLOSURE Example 1 Crosslinked Fracturing FluidMade with Produced Water

This example compared the rheologies of three different crosslinkedfracturing fluid systems: a standard borate crosslinked fresh waterfracturing fluid, a produced water sample including no pH adjustingbuffer, and a produced water sample including a pH adjusting buffer. Therheologies are shown in FIG. 3.

A standard borate crosslinked fracturing fluid (made in a fresh water)was prepared using the following:

a) a guar gum loading of 17 ppt

b) a pH buffer to adjust the fluid pH to above 9

c) a borate crosslinking solution

This combination of chemicals produced the rheology propertiesrepresented by the grey curve in FIG. 3. This curve shows a fracturingfluid system that may sustain a viscosity of ≥200 cps @ 100 sec⁻¹ forover two hours.

This test was then rerun after replacing the fresh water with a high TDSproduced back water sample. The produced back water had an analysis asfollows:

Property/Reagent Concentrations (mg/L) pH 7.05 TDS 99000 Total Hardnessas CaCO₃ 6200 Carbonate 0 Bicarbonate ≥2440 Alkalinity ≥2440 Chloride60000 H₂S 1 Bacteria SRB (cell/mL) 1000 APB (cell/mL) 1000 Calcium(Titration) 2240 Magnesium (Titration) 145.8 Boron (Hach) 43

Utilizing the same three components (from the fresh water test) and aproduced back fluid resulted in the rheology properties represented bythe dotted curve in FIG. 3. The results of this test confirm that theuse of a produced water prevents the development of any significantviscosity.

Finally, the effectiveness of utilizing the compositions, systems andmethods may be illustrated by using the same high TDS produced water inthe following modified procedure:

-   -   1. Weigh 350 (±0.5) grams of produced water base fluid into 1        liter blender glass jar.    -   2. Mix produced water base fluid on Constant Speed Blender at        2000 (±100) rpm.    -   3. Add 1.25 gpt of a low pH buffer or adjust produced water base        fluid to pH ˜4.5.    -   4. Measure 17 ppt POLYfrac Plus M4, a slurry of a guar gum in a        suspension package, (˜1.5 mL of slurry) in 3 mL syringe.    -   5. Inject 1.5 mL slurry into blender jar and mix for 3 minutes.    -   6. Measure and record viscosity on Fann 35 viscometer (w. R1B1)        or equivalent @ 300 rpm (511 sec⁻¹) for 1 minute and record pH.    -   7. Weigh 100 (±0.5) grams of linear gel into Pyrex 300 mL glass        beaker or equivalent.    -   8. Place beaker under overhead mixer and mix gel at 1000 (±50)        rpm with high efficiency mixing blade.    -   9. Add 1.8 gpt BBXL, a borate based crosslinker, (0.18 mL) and        promptly add 1.4 gpt

Catalyst Activator, a pH buffer that is used to adjust the final pH ofthe fracturing fluid, (0.14 mL) into the gel solution.

-   -   11. Mix gel until crosslinking    -   12. Promptly weigh 50 (±0.5) grams of crosslinked gel into cup        and place it on Grace M5600 HTHP viscometer or equivalent.    -   13. Run test at 140° F. for 2 hours.    -   14. Record crosslinked gel pH and post crosslinked gel pH.

The dashed curve in FIG. 3 illustrates the test results from thecompositions, systems and methods of this disclosure. The test resultsverify the ability to reach a high viscosity that is stable at 250 cps @for at least 2 hours that is comparable if not superior to the freshwater test results.

Example 2 Composition and System Behavior

A variety of compositions of this disclosure was tested. The sameapproach utilized in Example 1 was repeated for each composition toillustrate the effectiveness of this approach. The results of thesetests are illustrated in FIG. 4.

The graph illustrates the results of utilizing the previously describedcompositions of the disclosure to generate a two hour viscosity that iscomparable to what is achieved when using a fresh water. The eightproduced water sources covered a TDS range from about 60 ppm to about120,000 ppm. But even more important than the TDS was the presence ofmeasurable amounts of ions (for example boron) that have historicallybeen known to present major issues in creating a crosslinked fracturingfluid that exhibits the targeted viscosity and temperature stabilitythat is required when utilizing this type of fracturing fluid system.

Example 3 Shear History Effects

To measure proppant suspension properties of a polymer containingfracturing fluid (both before and after a shear history) in a dynamictest, the following procedure was developed:

-   -   a) hydrate the polymer (to be evaluated) for 5 minutes at 1500        rpm.    -   b) add 120 gm of 20/40 coated or uncoated sand (2 pounds per        gallon) and mix for 60 seconds at 1500 rpm. Note that the 120        grams would equate to 2 lb/gal if the test sample size is 500        mL.    -   c) lower the rpm until sand accumulates on the bottom of the        blender jar.    -   d) record the lowest rpm reading that does not cause sand        accumulation.

To establish the shear sensitivity of the test sample, the abovesequence was repeated by adding a high shear step (3 minutes @ 4500 rpm)between steps (b) and (c).

Using the above procedure (both with and without a shear step) withuncoated sand yielded the data shown in FIG. 5. The reported minimum rpmreflects the degree of dynamic movement necessary to keep the solids insuspension. The proppant is 20/40 uncoated sand.

These test results showed that a shear history resulted in a greaterthan 40% increase in measured minimum rpm (which equates to a >40%decrease in transport properties). Both standard and high molecularweight/viscosity friction reducers showed a level of shear degradation.However, when the standard friction reducers were exposed to arepresentative shear history, the result was a complete loss of proppanttransport properties (sheared standard friction reducers gave similarsuspension results to the base fluid without the addition of a polymer).The high molecular weight/viscosity friction reducer was damaged by arepresentative shear history, but still retained some measureableability to contribute to proppant transport. A linear gel was shown tonot be so shear degradable, but also was less effective (than the highviscosity friction reducer) in contributing to proppant transport.

Example 4 Shear History and Controlled Crosslinking

One option to low viscosity, high rate slick water treatment is toutilize the compositions, systems and methods of this disclosure tocreate a low polymer concentration crosslinked fracturing fluid thatwill exhibit a controlled viscosity increase and improved proppanttransport. This approach may be designed to accomplish the following:

-   -   a) generate relatively long narrow fractures or fracture        geometries,    -   b) improve proppant transport, which in turn leads to an        increase in propped fracture length,    -   c) potentially reduce an injection rate (which helps contain the        fracture growth within the targeted formation) and put away the        desired amount of proppant, and    -   d) reduce a volume of water that is required to create a desired        fracture geometry and place the proppant in the fracture.

Using a low polymer concentration (in this case 8 ppt polymer) anduncoated sand but with a specially formulated crosslinking mechanism hada substantial impact on controlling shear degradation of the crosslinkedpolymer system (as compared to the effects of high shear on the variousfriction reducers and linear gels that are frequently utilized in aslick water design). The suspension test results are shown in FIG. 6.The reported minimum rpm reflects the degree of dynamic movementnecessary to keep the solids in suspension. The proppant is 20/40uncoated sand.

FIG. 6 verifies the effect (that a representative shear history) has onthe ability to transport proppant. In each friction reducer test, theinclusion of a representative shear history resulted in a significantloss of the ability of the friction reducer to contribute to proppanttransport. However, a properly formulated low polymer concentrationcrosslinked fracturing fluid system accomplishes the desired goal ofachieving a substantial level of proppant transport despite experiencinga realistic shear history.

For a low polymer concentration polymer crosslinked fracturing fluidsystem to be suitably effective, initially the crosslinked structure(and its accompanying viscosity increase) should be delayed, but shouldbe established before the fracturing fluid slurry leaves the tubulardownhole injection mechanism and heads into the fracture field. Incertain embodiments, the crosslinking process is timed to occur in thelast 25% of its residence time in the wellbore tube. This would limitthe period of high shear that the crosslink structure is exposed tobefore the crosslinked fracturing fluid enters the relatively low shearenvironment that is characteristic of a fracturing fluid moving througha created fractured matrix. The crosslinked structure need not becompletely formed before the slurry enters the fracture, but thecrosslinking process desirably has gone far enough to have alreadyresulted in a substantial increase in viscosity that accompanies thedevelopment of the crosslinked structure and the associated contributionto improved proppant transport.

A Mechanism for Preventing Viscosity Degradation

While controlling the rate of crosslinking is certainly an effective wayto control the effects of shear degradation of low polymer concentrationcrosslinked fracturing fluids, it is not likely a total answer. The timea fracturing fluid takes to move through tubular mechanism for injectioninto a formation, a high shear period, may vary dramatically due to acombination of well depth, lateral length, and pump rate. Thus, tobetter preserve the proppant transport capabilities of the low polymerconcentration crosslinked fracturing fluids, a second mechanism may beincorporated that protects the fracturing fluid system against sheardegradation. Shear degradation in certain situations adversely affectsthe ability for low polymer concentration crosslinked fracturing fluidsto maintain viscosity and transport proppant capabilities. The addedprotection mechanism (when utilizing relatively low TDS water) includesutilizing a mixture of a guar or a guar derivative or a mixture thereofwith a high molecular weight anionic polyacrylamide >15 million. Theapproach was tested using a mixture of guar (4550) and friction reducer(identified as AFRD-12) to achieve the desired combination ofrheological properties and proppant transport. When utilizing high TDSwater (for the fracturing fluid) it may still be possible to utilize ahigh molecular weight anionic polyacrylamide but it may be necessary toreplace this polyacrylamide with either a cationic, non-ionic oramphoteric polyacrylamide.

Example 5 Maximum Transport Systems

To illustrate this approach, the following tests were performed. Thefirst set of tests (Table I) were performed using an initial 3 minutehigh shear period to simulate the trip from the surface to the fractureopening, while the second set of tests (Table II) were performed withoutthe initial 3 minute high shear period. These so-called MaximumTransport Systems (MTS™, a trademark of PfP Industries) are fracturingfluids including a mixture of a guar, guar derivative or mixture thereofand a friction reducer (FR) that is crosslinked to achieve maximalproppant transport properties.

TABLE I Tests of Fracturing Fluids Including a Guar and a FrictionReducer Without an Initial High Shear Period Hydration Test Guar† FR‡Viscosity Temp n′ Visc @ 100(1/s) cP # (ppt) (ppt) (cP) (° F.) 3 min 30min 60 min 3 min 30 min 60 min 23 7 1 5.6 75 0.5565 0.7897 0.7835 29.536.68 40.16 24 7 1 5.6 120 0.2857 0.4859 0.5424 21.79 49.29 46.71 25 7 15.6 120 0.2269 0.4327 0.4822 23.85 44.51 41.39 28 7 0 4.4 75 0.43330.7805 0.7935 16.19 13.04 16.33 29 7 0 4.4 120 0.3305 0.9279 1.0106 15.224.91 24.58 30 7 0 4.4 120 0.3049 1.3651 1.4849 13 17.47 17.9 31 8 0 5.080 0.5993 0.6097 0.7045 22.61 22.65 28.86 34 8 0 5.0 120 0.5679 0.35070.2994 17.63 48.08 47.98 35 8 0 5.0 120 0.4305 0.3180 0.3862 16.65 45.4146.4 wherein †4550 Guar is a high viscosity guar gelling agent availablefrom available from PfP Industries and ‡AFRD-12 is a dry anionic highviscosity friction reducer available from PfP Industries.

Looking at Test # 24 and Test # 34, the data suggests that there islittle difference between a 7:1 (guar:FR) mix and just using 8 ppt guar.However, the results may have been influenced by the fact that at 8 pptof 4550 guar, the fracturing fluid may be getting too close to aconcentration of guar that acts more like a conventional crosslinkedsystem. Looking at Test #24 and Test #29, comparing a fracturing fluidbased on a 7:1 guar:FR mixture to a fracturing fluid based on a 7:0guar:FR mixture, the data suggests that the FR is contributing to theviscosity building in an unexpected way. To better characterize theeffect of FR on viscosity building, Test #24 and Test #29 were rerun,but without the initial high shear period. If the viscosity is not verydifferent in the two runs, then the result would support the conceptthat an FR really does not impact the viscosity building or crosslinkedviscosity of a fracturing fluid. However, because the original resultsof Test #24 and Test #29 were so different, it may support the conceptthat the addition of the selected FR protects a 7 ppt crosslinked guarfracturing fluid from shear degradation.

To see whether a mixture of a guar and a friction reducer in afracturing fluid has no effect on viscosity building or a marked effecton viscosity building, several of the tests of Table I, where repeated,but without the initial high shear period.

TABLE II Tests of Fracturing Fluids Including a Guar and a FrictionReducer Without an Initial High Shear Period @ 120° F. Hydration TestGuar† FR‡ Viscosity Buffer DXL-2 n′ Visc @ 100(1/s) cP # (ppt) (ppt)(cP) (gpt) (ppt) 5 min 30 min 60 min 5 min 30 min 60 min 98 7 0 4.2 14.8 0.7965 0.6101 0.6654 42 38 38 104 7 1 5 1 4.8 0.8942 0.5937 0.668569 44 42 100 8 0 4.8 1 4.8 1.0118 0.3084 0.2933 69 52 52 102 8 1 5.4 14.8 0.8345 0.4813 0.502 85 70 70 wherein †4550 Guar is a high viscosityguar gelling agent available from available from PfP Industries and‡AFRD-12 is a dry anionic high viscosity friction reducer available fromPfP Industries.

When looking at Test #24 and Test #29 of Table I, which included ainitial high shear period, the 7:1 formulation had approximately twicethe viscosity @ 1 hour as did the 7:0 formulation. When looking at Test#98 and Test #104 of Table II, which did not include an initial highshear period, the 7:1 formulation showed about 10% increase in viscosity@ 1 hour compared to 7:0 formulation.

Comparing Test #24 to Test #104 verifies that the inclusion of 1 ppt ofthe AFRD-12 friction reducer transforms the formulation into afracturing fluid system that is unaffected by high shear. Test #24 ofTable I, which was exposed to an initial high shear period, actuallyexhibited a higher 60 minute viscosity of 46.7 cP compared Test #104,which was not exposed to the initial high shear period, which had a to60 minute viscosity of 42 cP.

The results of Test #98 and Test #104 of Table II both showed 60 minuten′ values below 0.7, while the results of Test #24 and Test #29 of TableI showed that when the 7:1 formulation (Test #24) is subjected to theinitial high shear period, the formulation had a low n′ (0.542), while,even though the 7:0 formulation (Test #29) exhibited a 60 minuteviscosity >24 cP, its 60 minute n′ was >1 (an indication that the fluidmay not have the desired crosslinked structure to maximize proppanttransport).

The results from Test #100 of Table II compared to Test #34 of Table Iconfirms that a 8:0 formulation is fairly resistant to sheardegradation. The inclusion of the initial high shear period only droppedthe 60 minute viscosity reading by ±8%.

Example 6 Dynamic Proppant Transport in a Crosslinked Fracturing FluidPrepared from High TDS Produced Back Water Base Fluids

Having established in Example 2 that the disclosed compositions, systemsand methods of this disclosure may generate desired rheologicalproperties using a high TDS produced back water base fluid, it isimportant to determine if in a low polymer concentration crosslinkedfracturing fluid system may exhibit a substantial proppant transportcapability even when subjected to a representative shear history andutilizing a high TDS water base fluid. FIG. 7 represents the suspensiontest results of the low polymer concentration crosslinked fracturingfluid approach and a variety of friction reducers in two different highTDS base fluids. In each case test, the suspension test included arepresentative shear history.

Clearly the combination of a representative shear history and elevatedTDS render all friction reducers incapable of contributing to proppanttransport (with the suspension test results being essentially the sameas measured with a brine containing no polymer). However, with this testapproach, the low polymer crosslinked fracturing fluid system (based onthe embodiments, systems and methods of this disclosure) still exhibitsa substantial ability to transport proppant.

Example 7 Friction Reduction

There are two more fracturing fluid characteristics that are consideredto be important for a low concentration crosslinked polymer fracturingfluid system to exhibit if the system was going to be used in place of afriction reducer polymer in a slick water fracturing fluid. The firstsuch characteristic is drag reduction. The one thing a friction reducerdoes well is reduce pipe friction that is created when the fracturingfluid and proppant are pumped through injection tubulars.

The conventional industry-accepted way to determine the amount of dragreduction (that a friction reducer may create) is with a devicedescribed as a flow or friction loop. An example of such a device isshown in FIG. 8.

The device includes a pump and a length of pipe with pressure taps thathave been designed to allow the fluid velocity in the test to berepresentative of what may be achieved in a fracturing treatment. Bymonitoring the pressure drop in the test section and comparing the testresults of pumping water with and without a friction reduction polymer,one may calculate the expected drag reduction that the addition of a thepolymer may achieve.

If a low concentration polymer crosslinked fracturing fluid system is tobe effective in replacing a slick water treatment design, it needs toyield similar drag reduction results. FIG. 9 shows the results of a dragreduction test comparing the drag reduction properties of a standardanionic friction reducer, a high molecular/high viscosity frictionreducer and the low polymer concentration crosslinked fracturing fluid.All three samples gave between 70% and 75% drag reduction and wherestable through the duration of the test cycle.

The present compositions, systems and methods are significantlydifferent than the industry standards which use normal guar and boratebased cross-linkers. Our process and chemistry works with a wide rangeof TDS base fluids that are obtained using a variety of produced waters,flow back waters, frac flow back waters, brine brackish waters, ORwaters, or mixtures thereof In certain embodiments, the base fluids mayalso include fresh water.

All references cited herein are incorporated by reference. Although thedisclosure has been disclosed with reference to its preferredembodiments, from reading this description those of skill in the art mayappreciate changes and modification that may be made which do not departfrom the scope and spirit of the disclosure as described above andclaimed hereafter.

1. A fracturing fluid composition comprising: a base fluid comprisingfresh water, an elevated total dissolved solids (TDS) water selectedfrom the group consisting of produced water, flow back water, brackishwater, reverse osmosis (RO) reject water, clear brine, or mixtures andcombinations thereof, one or more dry powdered gel-forming hydratablepolymers, a friction reducer composition, a cross-linking composition inan amount sufficient to crosslink the one or more gel-forming hydratablepolymers to form crosslinked structures within the fracturing fluidcomposition, and a proppant, wherein: the one or more dry powderedgel-forming hydratable polymers are present in an amount of less thanabout 10 ppt of the fracturing fluid composition, the friction reducercomposition is adapted to reduce drag properties of the fracturing fluidcomposition and to protect and stabilize the crosslinked structures fromshear degradation as the fracturing fluid composition travels down atubular downhole injection mechanism into subterranean formationfractures forming during fracturing, and the fracturing fluidcomposition is adapted to improve proppant transport properties, tocontrol viscosity when the hydrating fluid is a brine or a water havingelevated total dissolved solids (TDS), and to increase proppantconcentrations within fractures.
 2. The composition of claim 1, furthercomprising: a first buffer in an amount sufficient to adjust a pH of thefracturing fluid composition to an acidic pH to improve hydration of thehydratable polymers and to prevent premature crosslinking of thegel-forming hydratable polymers for base fluids containing crosslinkingions, wherein the acidic pH is less than or equal to pH 7, or less thanor equal to pH 6, or less than or equal to pH 5, or less than or equalto pH 4, and a second buffer in an amount sufficient to adjust theacidic pH to a final pH at or above pH 9 and sufficient to activate thecrosslinking composition to form the crosslinked structures.
 3. Thecomposition of claim 1, further comprising: an amount of a buffersufficient to adjust a pH of the fracturing fluid composition to a pH ator above 9 and to activate the crosslinking composition to form thecrosslinked structures.
 4. The composition of claim 1, wherein thecrosslinking composition is capable of producing the crosslinkedstructures at an acidic pH, wherein the acidic pH is less than or equalto pH 7, or less than or equal to pH 6, or less than or equal to pH 5,or less than or equal to pH
 4. 5. The composition of claim 1, whereinthe dry powdered gel-forming hydratable polymers are selected from thegroup consisting of galactomannan gums, glucomannan gums, guars,derivatized guars, cellulose derivatives, and mixtures or combinationsthereof.
 6. The composition of claim 5, wherein the friction reducercomposition comprises: one or more dry powdered synthetic polymersselected from the group consisting of the partially hydrolyzed polymersand copolymers are selected from the group consisting of hydrolyzed orpartially hydrolyzed polyacrylic acid, hydrolyzed or partiallyhydrolyzed polymethacrylic acid, hydrolyzed or partially hydrolyzedpolyacrylamide, hydrolyzed or partially hydrolyzed copolymers of acrylicacid and one or more ethylenically unsaturated monomers, hydrolyzed orpartially hydrolyzed copolymers of methyacrylic acid and one or moreethylenically unsaturated monomers, hydrolyzed or partially hydrolyzedcopolymers of acrylamide and one or more ethylenically unsaturatedmonomers and mixtures or combinations thereof, the ethylenicallyunsaturated monomers including vinyl alcohol, ethylene, propylene, andmixtures or combinations thereof, and/or one or more dry powderedanionic, cationic, or amphoteric homopolymers, copolymers, terpolymers,or high order mixed monomer polymers synthesized from one or moreanionic monomers, cationic monomers, neutral monomers, or mixtures andcombinations thereof, the anionic monomers are selected from the groupconsisting of acrylic acid, methacrylic acid,2-acrylamide-2-methylpropane sulfonic acid, maleic anhydride, andmixtures or combinations thereof, the cationic monomers are selectedfrom the group consisting of dimethyl-diallyl ammonium chloride,dimethylamino-ethyl methacrylate, allyltrimethyl ammonium chloride, andmixtures or combinations thereof, the neutral monomers are selected fromthe group consisting of butadiene, N-vinyl-2-pyrrolidone, methyl vinylether, methyl acrylate, maleic anhydride, styrene, vinyl acetate,acrylamide, methyl methacrylate, acrylonitrile, and mixtures orcombinations thereof, and the one or more synthetic polymers and/or theone or more anionic, cationic, or amphoteric homopolymers, copolymers,terpolymers, or high order mixed monomer polymers are also adapted toprotect and stabilize the crosslinked structures from shear degradation.7. The composition of claim 6, wherein the one or more syntheticpolymers and/or the one or more anionic, cationic, or amphoterichomopolymers, copolymers, terpolymers, or high order mixed monomerpolymers have molecular weights above about 15 million, or rangingbetween about 18 million and about 40 million, or ranging between about18 million and about 25 million.
 8. The composition of claim 1, whereinthe crosslinking composition comprises one or more compounds includingboron-containing ions, zirconium-containing ions, andtitanium-containing ions, or mixtures thereof.
 9. The composition ofclaim 1, wherein the hydratable polymer composition is present in aslurry in an amount between about 1 gpt and about 10 gpt provided thatthe one or more dry powdered gel-forming hydratable polymers are presentin an amount of less than about 10 ppt of the fracturing fluidcomposition.
 10. A fracturing fluid composition comprising: a base fluidcomprising fresh water, an elevated total dissolved solids (TDS) waterselected from the group consisting of produced water, flow back water,brackish water, reverse osmosis (RO) reject water, clear brine, ormixtures and combinations thereof, one or more dry powdered gel-forminghydratable polymers, a friction reducer composition, a cross-linkingcomposition in an amount sufficient to crosslink the one or moregel-forming hydratable polymers to form crosslinked structures withinthe fracturing fluid composition, and a proppant, wherein: the one ormore dry powdered gel-forming hydratable polymers are represent in anamount of less than about 10 ppt of the fracturing fluid composition,the friction reducer composition is adapted to reduce drag properties ofthe fracturing fluid composition and to protect and stabilize thecrosslinked structures from shear degradation as the fracturing fluidcomposition travels down a tubular downhole injection mechanism intosubterranean formation fractures forming during fracturing, and thefracturing fluid composition is adapted to improve proppant transportproperties, to control viscosity when the hydrating fluid is a brine ora water having elevated total dissolved solids (TDS), and to increaseproppant concentrations within fractures.
 11. The composition of claim10, further comprising: a first buffer in an amount sufficient to adjusta pH of the fracturing fluid composition to an acidic pH to improvehydration of the hydratable polymers and to prevent prematurecrosslinking of the gel-forming hydratable polymers for base fluidscontaining crosslinking ions, wherein the acidic pH is less than orequal to pH 7, or less than or equal to pH 6, or less than or equal topH 5, or less than or equal to pH 4, and a second buffer in an amountsufficient to adjust the acidic pH to a final pH at or above pH 9 andsufficient to activate the crosslinking composition to form thecrosslinked structures.
 12. The composition of claim 10, furthercomprising: an amount of a buffer sufficient to adjust a pH of thefracturing fluid composition to a pH at or above 9 and to activate thecrosslinking composition to form the crosslinked structures.
 13. Thecomposition of claim 10, wherein the crosslinking composition is capableof producing the crosslinked structures at an acidic pH, wherein theacidic pH is less than or equal to pH 7, or less than or equal to pH 6,or less than or equal to pH 5, or less than or equal to pH
 4. 14. Thecomposition of claim 10, wherein the dry powdered gel-forming hydratablepolymers are selected from the group consisting of galactomannan gums,glucomannan gums, guars, derivatized guars, cellulose derivatives, andmixtures or combinations thereof.
 15. The composition of claim 14,wherein the friction reducer composition comprises: one or more drypowdered synthetic polymers selected from the group consisting of thepartially hydrolyzed polymers and copolymers are selected from the groupconsisting of hydrolyzed or partially hydrolyzed polyacrylic acid,hydrolyzed or partially hydrolyzed polymethacrylic acid, hydrolyzed orpartially hydrolyzed polyacrylamide, hydrolyzed or partially hydrolyzedcopolymers of acrylic acid and one or more ethylenically unsaturatedmonomers, hydrolyzed or partially hydrolyzed copolymers of methyacrylicacid and one or more ethylenically unsaturated monomers, hydrolyzed orpartially hydrolyzed copolymers of acrylamide and one or moreethylenically unsaturated monomers and mixtures or combinations thereof,the ethylenically unsaturated monomers including vinyl alcohol,ethylene, propylene, and mixtures or combinations thereof, and/or one ormore dry powdered anionic, cationic, or amphoteric homopolymers,copolymers, terpolymers, or high order mixed monomer polymerssynthesized from one or more anionic monomers, cationic monomers,neutral monomers, or mixtures and combinations thereof, the anionicmonomers are selected from the group consisting of acrylic acid,methacrylic acid, 2-acrylamide-2-methylpropane sulfonic acid, maleicanhydride, and mixtures or combinations thereof, the cationic monomersare selected from the group consisting of dimethyl-diallyl ammoniumchloride, dimethylamino-ethyl methacrylate, allyltrimethyl ammoniumchloride, and mixtures or combinations thereof, the neutral monomers areselected from the group consisting of butadiene, N-vinyl-2-pyrrolidone,methyl vinyl ether, methyl acrylate, maleic anhydride, styrene, vinylacetate, acrylamide, methyl methacrylate, acrylonitrile, and mixtures orcombinations thereof, and the one or more synthetic polymers and/or theone or more anionic, cationic, or amphoteric homopolymers, copolymers,terpolymers, or high order mixed monomer polymers are also adapted toprotect and stabilize the crosslinked structures from shear degradation.16. The composition of claim 15, wherein the one or more syntheticpolymers and/or the one or more anionic, cationic, or amphoterichomopolymers, copolymers, terpolymers, or high order mixed monomerpolymers have molecular weights above about 15 million, or rangingbetween about 18 million and about 40 million, or ranging between about18 million and about 25 million.
 17. The composition of claim 10,wherein the crosslinking composition comprises one or more compoundsincluding boron-containing ions, zirconium-containing ions, andtitanium-containing ions, or mixtures thereof.
 18. The composition ofclaim 10, wherein the hydratable polymer composition is present in aslurry in an amount between about 1 gpt and about 10 gpt provided thatthe one or more dry powdered gel-forming hydratable polymers are presentin an amount of less than about 10 ppt of the fracturing fluidcomposition.
 19. A method of fracturing a subterranean formationcomprising: pumping a fracturing fluid composition into a tubulardownhole injection mechanism and into a formation to produce fractureswithin the formation, wherein the fracturing fluid compositioncomprising: a base fluid comprising fresh water, an elevated totaldissolved solids (TDS) water selected from the group consisting ofproduced water, flow back water, brackish water, reverse osmosis (RO)reject water, clear brine, or mixtures and combinations thereof, one ormore dry powdered gel-forming hydratable polymers, a friction reducercomposition, and a cross-linking composition in an amount sufficient tocrosslink the gel-forming hydratable polymer to form crosslinkedstructures in the fracturing fluid composition, wherein: the one or moredry powdered gel-forming hydratable polymers are represent in an amountof less than about 10 ppt of the fracturing fluid composition, thefriction reducer composition is adapted to reduce drag properties of thefracturing fluid composition and to protect and stabilize thecrosslinked structures from shear degradation as the fracturing fluidcomposition travels down a tubular downhole injection mechanism intosubterranean formation fractures formed during fracturing, and thefracturing fluid composition is adapted to improve proppant transportproperties, to control viscosity when the hydrating fluid is a brine ora water having elevated total dissolved solids (TDS), and to increaseproppant concentrations within fractures.
 20. The method of claim 19,further comprising: adding a proppant to the fracturing fluidcomposition, and wherein the pumping generates long narrow fractures inthe formation and increases proppant concentrations within the longnarrow fractures.
 21. The method of claims 19, wherein, in the pumpingstep, the fracturing fluid composition further comprising: a firstbuffer in an amount sufficient to adjust a pH of the fracturing fluidcomposition to an acidic pH to improve hydration of hydratable polymersand to prevent premature crosslinking of the gel-forming hydratablepolymers for base fluids containing crosslinking ions, wherein theacidic pH is less than or equal to pH 7, or less than or equal to pH 6,or less than or equal to pH 5, or less than or equal to pH 4, and asecond buffer in an amount sufficient to adjust the acidic pH to a finalpH and to activate the crosslinking composition, wherein the final pH isat or above
 9. 22. The method of claims 19, wherein, in the pumpingstep, the fracturing fluid composition further comprising: a buffer inan amount sufficient to adjust a pH of the fracturing fluid compositionto a final pH and to activate the crosslinking composition to form thecrosslinked structure, wherein the final pH is at or above
 9. 23. Themethod of claims 19, wherein, in the pumping step: the crosslinkingcomposition is capable of producing the crosslinked structures at anacidic pH, wherein the acidic pH is less than or equal to pH 7, or lessthan or equal to pH 6, or less than or equal to pH 5, or less than orequal to pH
 4. 24. The method of claims 19, wherein, in the pumpingstep: the dry powdered gel-forming hydratable polymers are selected fromthe group consisting of galactomannan gums, glucomannan gums, guars,derivatized guars, cellulose derivatives, and mixtures or combinationsthereof.
 25. The method of claims 24, wherein, in the pumping step, thefriction reducer composition comprises: one or more dry powderedsynthetic polymers selected from the group consisting of the partiallyhydrolyzed polymer and copolymers are selected from the group consistingof hydrolyzed or partially hydrolyzed polyacrylic acid, hydrolyzed orpartially hydrolyzed polymethacrylic acid, hydrolyzed or partiallyhydrolyzed polyacrylamide, hydrolyzed or partially hydrolyzed copolymersof acrylic acid and one or more ethylenically unsaturated monomers,hydrolyzed or partially hydrolyzed copolymers of methyacrylic acid andone or more ethylenically unsaturated monomers, hydrolyzed or partiallyhydrolyzed copolymers of acrylamide and one or more ethylenicallyunsaturated monomers and mixtures or combinations thereof, theethylenically unsaturated monomers including vinyl alcohol, ethylene,propylene, and mixtures or combinations thereof, and/or one or more drypowdered anionic, cationic, or amphoteric homopolymers, copolymers,terpolymers, or high order mixed monomer polymers synthesized from oneor more anionic monomers, cationic monomers, neutral monomers, ormixtures and combinations thereof, the anionic monomers are selectedfrom the group consisting of acrylic acid, methacrylic acid,2-acrylamide-2-methylpropane sulfonic acid, maleic anhydride, andmixtures or combinations thereof, the cationic monomers are selectedfrom the group consisting of dimethyl-diallyl ammonium chloride,dimethylamino-ethyl methacrylate, allyltrimethyl ammonium chloride, andmixtures or combinations thereof, the neutral monomers are selected fromthe group consisting of butadiene, N-vinyl-2-pyrrolidone, methyl vinylether, methyl acrylate, maleic anhydride, styrene, vinyl acetate,acrylamide, methyl methacrylate, acrylonitrile, and mixtures orcombinations thereof, the one or more synthetic polymers and/or one ormore anionic, cationic, or amphoteric homopolymers, copolymers,terpolymers, or high order mixed monomer polymers have molecular weightsabove about 15 million, or ranging between about 18 million and about 40million, or ranging between about 18 million and about 25 million, andthe one or more synthetic polymers and/or one or more anionic, cationic,or amphoteric homopolymers, copolymers, terpolymers, or high order mixedmonomer polymers are adapted to also protect and stabilize thecrosslinked structures from shear degradation.
 26. The method of claim19, wherein, in the pumping step: the crosslinking composition comprisesone or more compounds including metal ions selected from the groupconsisting of boron, zirconium, and titanium, and mixtures thereof, andthe proppant comprises 20-40 mesh sand.
 27. The method of claims 19,wherein, in the pumping step, the hydratable polymer composition in ispresent in a slurry in an amount between about 1 gpt and about 10 gptprovided that the one or more dry powdered gel-forming hydratablepolymers are present in an amount of less than about 10 ppt of thefracturing fluid composition.